Multihull Structure Thoughts

This photo of Mama Tried is pretty spectacular. I wish I had paid more attention when I had the chance. I never liked the look of the ama's and I wonder what the consensus was about the new ama's over the originals.

 

The following is in response to a request about Schionning Multiply 850 and 1030 catamarans. The only reference found was on the Wayback machine that had no diagrams. There is little information about Schionning plywood boats as he moved into strip plank cedar and flat panel duflex/balsa fairly early to improve the build quality and resale value of his designs. The earliest reference I could find to a plywood Schionning was an early 930 cat built in the 90’s. The magazine article said it was plywood but no specifications. One photo showed stringers in the hulls and I suspect it had taped seams for the multi chine hulls. There is an article in Multihull World magazine Nbr 37 and 38 of an open wingdeck 930 called “The Immaculate Conception” in 1997 and looked like a plywood cat. Paul Nudd knew the boat and may be able to verify that.

So, assuming that the Wilderness 930 and 1030 designs had their foundations in the Multiply designs we will focus on those designs. Both cats started as multichine designs and both designs were converted into the strip plank cedar Cosmos 930 and 1030 cat designs. They had the same or similar layouts and variation of displacement depending on the build materials.

The Wilderness 930 and 1030 hull shapes were multi chine and remained basically the same shape irrespective of the claimed displacement. So, in the Wilderness 1030 plywood version had a displacement of 8,160 lbs whereas the Wilderness 1030 built in cored materials had a displacement of 7,160 lbs. The Wilderness 930/Cosmos 930 displaced 5,900 lbs. As you will see from the various PDF’s of the Wilderness 1030 and Cosmos 1030 there were various “versions” of the same boat with various names and designations EG there was a 1030, a 1040 and a 1050 all basically the same design. The real difference was in the structure. The plywood boat would had plywood bulkheads, the first strip plank cedar versions still had plywood bulkheads but some unidirectional e-glass flanges. The Duflex or balsa cored boats had cored bulkheads and e-glass flanges initially. Now Schionning does carbon fibre flanges on cored cross beam structures.

It’s a pity that these designs are no longer available, as this size of cat is wanted by many. They were bridge deck cats with berths, galley, toilet and main cabin. But I suspect the real reason this size of cat is not available is Schoinning business model of plans plus a kit to build a boat is very profitable in larger size cats (40 foot plus). Why do smaller designs if the profit margin is less but the owner builder still requires the same amount of support as larger designs.

As there are no accessible study plans for the 930 I will provide some basic dimensions. The 930 is 30.5 x 19.5 foot weighing 2,700 lbs and displacing 5,900 lbs. It carries a fractional rig with a 39.5 foot aluminium mast with a 350 square foot mainsail and 200 square foot fore triangle. The length to beam of the hulls is 12:1. The original boat was flat panel, the Cosmos 930 is strip plank Western Red Cedar. The 12 mm WRC had about 446 gsm 45/45 e glass on either side in epoxy. Some boats were done with 400 gsm 45/45 on outside and 200 gsm uni on the inside. The main cross beam were timber framed plywood web faces with unidirectional e-glass top and bottom flanges. The rear beam is similar. The remaining bulkheads were plywood. The Wilderness 930 was born. The Wilderness is a multi chine flat panel build with mainly 13 mm Duflex balsa panels. The panels are put in female frames and taped together then have an additional layer of glass over the outside and inside. The bulkheads and cross beams are again Duflex with the initial boats having e glass unidirectional flanges, later boats had carbon fibre glass around the edges to provide strength.

The jpegs and multiple PDF’s provide some idea into these designs. The 930 first and 1030 second. If you are interested in the 1030 read all 3 PDFs as each has different details about the design.

 

Hi. In reference to the Wilderness 1030 PDF's please read all 3 Wilderness 1030 PDF's. The Wilderness 1030 studyplans give the most detail and drawings. The NewWilderness 1030Part2A contains the largest drawings and some photos of the 1030. Each has value but the last 2 PDF's are of more value.

 

Once you could sail rings around a 40 foot monohull in a good Farrier tri, now the latest racing Class 40 can peak at 25 knots and do 17 knot averages for 24 hours (415 miles in 24 hours) and hold 20 knot averages for an hour under auto pilot when shorthanded. Class 40 monohulls are limited by a set of rules which are 40 x 14.75 foot with a maximum draft of 9.85 foot. The minimum weight is 10,080 lbs. The mast is 62.3 foot with a sail area of about 1240 square foot. There can be no additional foils beyond the keel and 2 rudders. Therefore two 750 litre water tanks (1,670 lbs weight per tank) and beam are the only things to give righting moment to offset the large rig. The original Class 40 boats had a conventional fine bow wide stern shape. In about 2016/17 under the influence of David Raison race winning 21 foot Mini Transat mono’s several designers included Raison designed very wide bow (scow bow) Class 40 mono’s.

Like all traditional yachting, the Class 40 guys put in a rule to ensure the boats had a pointy bow and said the boat must be a maximum width on deck 200 mm aft of the bow. The designers meet the rule by having a rounded forward bottom and a pointy bit that meet the rule requirements well above the sailing waterline. Why did the designers do this? There is one thing you need when you are carrying very large rigs. Stability. You get stability by beam. If you can get your boat to heel and ride on one edge of the hull and that hull edge is nearly the full length of the boat you end up with maximum stability. It is a monohull when heeled has a slim “catamaran” type hull with minimal wetted surface.

This approach to monohull design has 2 main weaknesses. The first is wetted surface in light airs (below about 6 knots). Massive very efficient rigs help solve this issue a little, but brute sail area and an ability to sail faster than wind speed to induce some heeling moment (reducing wetted surface) helps enormously to overcome this weakness. Second problem is big fat bows on monohulls do not go well upwind. The bow shapes on the Class 40 boats are getting better as designers optimise the shape but you are losing performance upwind compared to more conventional shapes. Some Class 40 races are still won by finer bow older boats when there is a majority of upwind work. But the speed advantage of the wide bow scow shapes in reaching conditions generally offsets any upwind disadvantage.

The initial concept of the Class 40 rules was to minimise cost, so the rules remain restrictive in terms of hull materials (epoxy- foam glass) and appendages (no foils), it does little to control the sails and on-board electronics. In the end, the budgets have become quite high with capital costs ranging from 410,000 to 650,000 euros and operating budgets exceed 500,000 euros per year for the top boats. The costs may be “high” but there is 180 plus Class 40 boats launched so far, and the enthusiasm for the class is growing.

To give you a real feel for Class 40 performance, on some race courses they can beat IMOCA 60 foot monohull racers (without foils) boat for boat. These are very fast boats. As Ross Hobson the ex-owner of Mollyhawk a 40 foot racing tri said 5 years ago, he sold Mollyhawk when the 40 foot racing monohulls could beat it around a race course.

The jpegs give you the idea. The first jpeg is a comparison between the older shape (white) and new shape (grey). The latest boats have more aggressive bows than the first jpeg “boat”.

 

The Tristar 18 was designed in the late 1960’s by Ed Horstman. The Tristar 18 is 17.7 x 12.1 foot (foldable to 8 foot for trailing) and weighed about 600 lbs depending on the construction choice. The 30 foot wood or aluminium mast carries 194 square foot of sail in the upwind rig and a 310 square foot spinnaker could be added for downwind sailing. The main hull waterline length to beam is 9 to 1. The floats are 15 foot long with an average waterline length to beam of about 13 to 1. The main hull draws 200 mm and with daggerboard down draws 3 foot. A 2 HP outboard could power the tri if required.

The Tristar was conceived as a day sailor that could sail in bays and coastal conditions with 4 crew for fun. It was also promoted as a cheap camp cruiser for a couple as the trampolines were 7 foot long and could be used for berths. There was storage forward of the mast for your camping gear etc.

Now to the construction. Take your choice. Chine plywood for the main hull and floats. Double diagonal plywood construction on the main hull and chine plywood flats. Or in a later option, foam glass round bilge main and float hull. The main hull either had 6 mm plywood panels for the chine hull or 2 layers of 3 mm ply for the double diagonal construction. The bulkheads were 6 mm plywood with timber edging and wood stringers/chines. The floats were similar construction. These boats were strong but had 2 minor problems. The initial rudders were to short and needed to be deepened 150 mm and the tris used for racing had larger daggerboards to help the tri upwind. I do not know the specs of the foam glass version but in the days of the original design it would have contained CSM and polyester resin. Modern foam glass builds could be lighter, more waterproof and stronger. The cross beams are timber (about 150 x 65 mm) tapered toward the floats. There is aluminium or stainless steel plates at the fold points of the cross arms with pivot bolts to allow the floats to be folded upward.

The performance of the Tristar 18 varied according to the owner. One owner commented “I raced her once on Lake Texoma in winds gusting 30, reefed main, sitting out on the windward ama, all the way back next to the beam, crew next to me, the leeward float deck barely clearing the waves, speed over 15 knots, and when the unusual 5th or 7th wave hit watched the float go through the wave top, she could not point with the monohulls, but she had the speed and power to pass them.” Also “The Tristar 18 had floats that had a flat bottom, and with the rocker, at speed reaching they were like water skis lifting the leeward float to the surface.” There were other owner comments about a good handling vessel that could cruise very well with a bit of a load. This design was done when speed was reasonably good but load carrying capacity was also valued in a day sailor. Recent day sailor tri design have larger floats to improve performance, but the original Tristar 18 design floats are OK.

The jpegs give the idea. The "sail plan" jpeg is not the correct scale. The build is mainly of plywood chine hull. Some of the sailing jpegs are of round bilge options.

 

This is a short story about a good looking well shaped cat that I cannot find a jpeg for. The design is featured in Woodenboat Magazine December 2021 issue number 283. The “Martinet” cruising catamaran is a JF Bedard design. The "Martinet" is 35 x 17.8 foot with a displacement of 10,800 lbs and has a 41 foot mast with a fractional fat head main rig of 668 square foot. The hull length to beam is 10.6 to 1. The draft over the fixed low aspect ratio keels is 4 foot. The Martinet has a kickup central rudder off the back end of the wing deck.

The accommodation is sensible with 2 forward double bunks on the wingdeck, each with its own cabin and toilet. The main saloon has 6 foot headroom and a large seating area with a galley down stairs in a hull. The navigation area is in the other hull. So far every thing is sensibly proportioned and well designed.

Now the interesting items start to appear. On the bridge deck under the saloon seat is a 100 gallon of water. That is about 830 lbs that should be at least 3 foot lower in the hulls to help maximise stability. Next, having a kickup central rudder mounted on the wing deck seams a bit futile if the cat has a fixed 4 foot draft. 2 smaller spade rudders on the hulls will give redundancy and probably more control. But my real issue is with the construction.

The cat is basically plywood with strip plank cedar hulls. The bulkheads, deck and cabin are 12 mm plywood. Depending on the framing underneath the deck may be “right” or heavy. Most cats in this size range have 9 mm wood decks and cabin structures. The hulls are 16 mm bead and cove western red cedar strips with 260 gsm glass on the outside (460 gsm below the waterline) and NO glass fabric on the inside of the western red cedar strip plank hull. This is unique build approach to strip plank catamaran hulls to my knowledge.

2 issues. This concept works in monohulls with thicker WRC strips and more hull curvature. Cat hulls have minimal fore and aft curvature resulting in less stiffness and according to several designers and boat repairers I have spoken to of multihulls strip plank hulls, they break the glass fabric on the inside of the hulls when they have a serious knock. If there is no glass on the inside of the hull you have lost a significant amount of resistance to hull damage. Secondly the glass layup on the hull outside above the waterline is light. Cats in this size normally have a minimum of 400 gsm biax on both sides of the strip plank cedar. If you are interested in this design, ask some serious questions and do some serious research into hull structures.

The anticipated performance is an 11 knot boat in cruising mode and right conditions with higher peak speeds EG my estimate is 16 to 18 knots. This is a fast cruiser not a racer.

This is a well conceived cat with good proportions but I have reservations about its structure and rudder arrangements.

J Bedards other designs look good and I have included jpegs of J Bedard “Shankara” cruising catamaran design which is 44 x 24.2 foot with a displacement of 20,000 lbs in cruising trim and a sail area of 1,119 square foot. But “Martinet” drawings are only available in Woodenboat magazine 283 at this moment.

 

Wow and there I was thinking just uni’s on the inside was minimalist !

 

Ian Farrier spec'd uni over strip for his tris. I'm not overly concerned at the outside weights but I'd expect the same inside, and probably less timber. 16mm WRC is strong enough if you add uni inside to take impacts. Maybe 300gsm plus... The 12mm ply is heavy but maybe it was done to make decks less springy and eliminate some stringers. 12mm bulkheads are too heavy.

It sounds like his experience is monohulls and he's had a go at a cat but made it using mono structures... bit like the beneteau blue 2 which is one of the most awful cats I've ever seen...

 

The EOS 54 was designed by Christophe Barreau (who designed the TS 42) as a fast cruising cat. The cat is built by Marsaudon Composites. The EOS is 54.1 x 27.8 foot with a complete boat weight of 30,900 lbs and a displacement of 36,100 lbs. The 75 foot mast carries a 1085 square foot mainsail, 673 square foot self tacking solent, a 1,990 square foot asymmetric spinnaker and a mast head 2,500 square foot running spinnaker. The hull length to beam is about 12 to 1. The underwing clearance is 3.3 foot. The draft is 4.1 over the rudders and 9.7 foot over the daggerboards. Fixed keels are an option. There are two 55 HP diesel engines. As a comparison a Lagoon 560 displaces 67,000 lbs with fatter hulls and a similar rig.

The EOS 54 is a semi custom cat that can be had with 3 to 5 double berth cabins and 3 to 4 toilets depending on the intended function. The owner’s version has an entire hull to the owner. The charter version has smaller hull cabins but are still very useful. The main saloon containing a galley, dining and navigation. It is smaller than many of its competitors but has vertical windows which allow the use of the entire area. Also, a very large door opening allows the covered cockpit to be used as part of an extended main saloon to create a “larger” living space. Steering is done from spaces either side of the cockpit.

The EOS 54 performs very well according to test reports, being able to sail at just below wind speed in moderate conditions. If pushed this cat could achieve 300 mile days. Call it a high performance cruiser more than a toned down racer.

There are several versions of construction. The initial boat was a sandwich construction of foam glass / infused polyester and more cruising orientated. Later higher performance versions were foam glass / infused vinylester with additional Kevlar and carbon fibre as required. The simpler cruising version has more cabins which increases the weight and decreases the performance. The weight gain of the cruising over the performance version is limited to an additional 3000 lbs by limiting additional fittings and equipment.

A nice item on the fixed keel version (often the cruising option) is an automatic senor on the keel that releases all sails sheets when a hull lifts from the water. A good anti capsize approach but no reports of how effective it is.

The jpegs give the idea.

 

A story of a man who developed many proas trying to achieve a single handed sailing proa to suit himself. There are few dimensions in this item but a few good ideas. His initial interest was a commercially viable boat. It took ages to built, male plug, female mould and epoxy foam sandwich boat. In October 1987 he took part in the Speed Sailing Championships in Weymouth with his first proa. There were strong winds and the weakness in the design became brutally obvious. The proa could sail but was neither fast or in control. In an attempt to salvage something, he cut the sail in half to become a jib that could be pulled from bow to stern when shunting. Windsurfers were much faster. The first 2 jpegs are of the 1987 proa. He gave up dreams of production boats and got a real job.

After many years of playing around with other experimental boats, dinghies and canoes. He came back to proa’s in the early 2000’s. There were several design concepts but a conventional proa was built next. It was called Pjoa (Polish word for proa). The main hull was one of the canoe’s with a simple float and a crab claw rig. Pjoa sailed but was not easy to tack especially single handed. There were new design concepts to simplify the rig. The 2 mast concept was developed with a decent lee board for windward work but the canoe shaped main hull was still being used. After a few more design iterations there came the Spinlugger concept.

The Spinlugger included many new idea’s in both rig, sail control and steering control concepts. The rig featured a easy to tack lug rig that can also be moved fore and aft to help with steering control. The designer builder needed to build a light, cheap, simple experimental proa to prove some of the ideas.

The final jpeg gives the first build of the simple experimental proa. Tomorrow we will detail the build of the simple proa and subsequent thoughts.

 

Today we will focus on the TP 02 proa built by yesterday’s passionate proa person. He needed a simple experimental proa to prove a few of his ideas so he conceived a 15.7 x 7.2 foot proa with the main hull having a I foot beam and 1.45 foot hull depth. The 15.7 foot float has a 200 mm beam and 150 mm hull depth. The sail area is basically a large windsurfer rig with wishbone boom and supporting struts. All well so far. The steering system started with 2 leeboard that turned in to steerable rudder boards after some initial problems.

The hulls are constructed from 4 mm plywood with pine chine and gunnel logs and three 9 mm ply primary bulkheads in the hulls. There is a bulkhead under each beam and under the mast base. There are some secondary bulkheads as well. After some initial sailing there was some timber and carbon fibre reinforcing around the rudder mounts and main hull deck edge where the rudder boards attached to the hull.

The TP 02 version of the proa sailed reasonably well. To quote the owner “This was tested at Scaling Dam and….. well it worked. I could sail where I wanted to, shunt and was pretty much in control.” After further testing he decided to do some additional design time and a rerig of TP 02 to form a 2 master lug rig proa. The original TP 02 hulls were used but the boat was renamed TP 03. Essentially a mirror of TP02, two sails and one board. The board was mounted so it could move fore and aft along the side of the main hull. Two balanced lug sails on free standing masts were all built onto the TP02 platform. The sails are made of Polytarp and the seating platform was a gate. It worked. The sails could be trimmed independently so I could manoeuvre when stationary. The board was pulled to a set position, the forward sail cleated and by fine trim on the board position and aft sail steered the proa. After a period of serious testing to develop and evaluate the ideas he ended up with a relatively simple to control single handed proa.

To develop the design further he would need proper sails. The expense of proper sails would have been dubious on the ‘disposable’ hulls, so TP03 eventually went on the bonfire. The designer was now confident that he had successfully developed a working single handed proa, and had gotten the Proa itch out of his system for a while.

A few years later in 202o a series of new designs for tacking and conventional proa’s came forth, shown below, with a different rig concept. The rig concept is a simplified tacking arrangement that shifts the centre of effort as well as tacks the rig at the same time. There is no report of these designs being built or finalised.

Interesting development of a proa concept. Hopefully a later version will be built to test the ideas.

 

NEEL sailing trimarans decided to expand into the power trimaran market. They actually had the idea 15 years ago but only recently developed the project to reality. The architects are Nivelt and Frutschi. The LEEN 56 power trimaran is 56 x 27 foot with a weight of 48,000 lbs and a displacement of 70,000 lbs(there are varying numbers but I think these are the most realistic). The draft is 3.85 foot. The NEEL 56 is a pure cruising vessel deliberately designed to travel long distances at moderate speeds. The main engine is a 300-450 hp Cummins QSB6.7 with in port maneuvering facilitated by the two 15 kW electric motors placed in the floats. Fuel tanks total 5000 litres (1320 gallons) with specialised fuel filtering facilities in and out of the fuel tanks.

The claims of long range performance has been backed up by several tests reviews. The large power bank (22 kWh in 48 V lithium-ion Mastervolt batteries) as part of the “Hybrid Pack” allows you to motor for an hour at 4 to 5 knots without using the main engine. This is used for in port or low pollution area’s. The Cummins 305 HP engine runs between 1,800 and 2,000 rpm. The ideal boat speed is 9 knots, with a consumption of 4.75 US gal (18 liters)/hour, or half a gallon (2 liters) per nautical mile. A quick calculation of the range with the 1,320-gallon/5,000-liter tanks is 2,500 nautical miles. By easing off the throttle a little to 7/8 knots, you can exceed 4,000 nautical miles. The maximum speed is 11.5 knots consuming 88 litres/hour for a range of 650 miles.

The accommodation is good to very comfortable. Any vessel that has an owners cabin on the main deck and a toilet ensuite “downstairs” that is 14 foot long is comfortable. The rest of the tri has 3 large double berth cabins with attached toilets. There is a single berth “crew cabin” with attached toilet. The main cabin has a very large galley and seating/dinette arrangement which is next to the cockpit through a large open door. Forward of the main cabin is the separate steering cabin space with navigation and spare seating. The optional flybridge is vast. You could live permanently on this boat.

The build of this cat is a little unusual for a production boat. The majority of the vessel is built using vacuum infused foam glass flat panels made on 80 x 13 foot epoxy marble tables. Those flat panels are then put into a female frame for final construction. There are some female moulded rounded panels use in the tri where required. The forward cabin structure where there is a lot of windows is made in aluminium. All bulkheads and partitions are foam glass. The engine room is large and lined with 50 mm sound deadening material and lined with metal. The main materials are mainly E-glass, some carbon fibre and vinylester resin with Kevlar reinforcement in selected areas (eg underwater).

This is a solid cruising vessel capable of transatlantic runs. It is moderately cheap to run doing 200 mile days with comfort. This tri is not about 20 knot speeds to impress you mates but when you call your mates from 4000 miles away in the sun, I think they will be jealous. The jpegs give the idea.

 

Fred Barret yacht design is a Tasmanian (Australia) studio. Fred has worked for many companies (including Incat large commercial cats) ranging from building to designing before he went out on his own. He has designed a range of monohull and catamaran commercial and personal craft. The power catamaran shown here is used daily in tourist charter work around the bottom of Tasmania. The “Three Capes” tourist cat is 40 x 15.4 foot with a 27,000 lbs displacement. The length to beam on the hulls is 7.2 to 1. The cat has a draft of 2 foot. Power is four 250 HP outboards that use 100 litres/hour at cruising speed of 25 knots with a top speed of 43 knots. There is 2000 litres of fuel. The reason for the 4 engines is if there is a failure on 1 engine the cat can still function at cruise speed for the tour. As you will see in the jpegs this cat operates in some rough water in “interesting” locations.

There are 2 ways to design a power catamaran. One is to design fat semi planning hulls with minimal hull separation, then put a lot of engine HP and the cat will go fast but at a relatively high fuel consumption (still lower fuel consumption than a lot of mono’s doing the same speed). The other option is the Malcolm Tennant type cat designs with slim hulls reasonable hull separation. Tennant type cats have very low fuel consumption and are very efficient up to about 30 knots. The downside of the Tennant type cats is they have to be kept light and do not tolerate excessive overloads or major load shifts. A tourist boat may have 10 passengers or 30 passengers who may all be seated correctly or running to the bow to look at a whale etc. You sacrifice fuel economy for business reality.

Being a day tourist boat, it has seating for 30 passengers and 2 crew. There is a toilet beside the helming position. There are 3 ten person full life rafts and other safety equipment to meet all legal requirements.

The cats construction is basically aluminium with 5 mm hull sides and 6 mm hull bottom and underwing plate. There are full 10 width frames/bulkheads that are one metre (3.4 foot) apart with longitudinal stringers or chine steps that are effectively 330 mm apart on hull sides. The keel lines are 12 mm thick x 170 mm high. The cat was built in 15 weeks by professional builders under time and under budget.

The jpegs give the idea. A very interesting functional cat that does operate in rough water daily. These tours are not for the faint hearted.

 

The second Fred Barret yacht design is a 9 metre aluminium power work cat that could also form the base of a fast strong cruising cat. The cat is 29.5 x 10.2 foot. The weight is 12,300 lbs with full fuel tanks, the displacement is unknown. The hull length to beam is 8 to 1. The draft is 1.5 foot over the hull and 2.5 foot over the outboard leg. The two outboards are not specified but would be about 150 HP.

The original design was for a workboat for fishing or diving. But the design also had a small double berth cabin forward with space for a toilet and some stowage etc. The covered forward part of the cockpit has room for a small galley and helm position. The first 9 meter built (Seaducer 3, first jpeg) is a workboat, but there are jpegs of a 9 meter proposal with a larger deck cabin.

The 9 meter construction is basically aluminium with 5 mm hull sides and 6 mm hull bottom and underwing plate. Again, chine steps and stringers on the frames support the shell structure. The diagrams show its work boat nature with cranes capable of lifting 44 gallon drums etc for fishing output or loading ice etc. The study plans give the idea of construction and indicate the shape of the cat. There are other jpegs of a 8 meter and a 6.5 meter aluminium catamaran builds designed by Fred. There is a lot of common elements in these designs and builds.

Fred Barret has had many commercial aluminium vessels built but also does sailing monohulls for cruising and racing in composites or wood. He also has a 33 foot Tennant style power catamaran cruiser that is a proposal. We may look at that later. An interesting series of designs. The jpegs give the idea.

 

The only thing missing off the Neel is a Tuna tower, cheap skates.